U.S. patent application number 10/165512 was filed with the patent office on 2002-12-12 for optical module, alignment method of optical module, and alignment device of optical module.
This patent application is currently assigned to Nippon Sheet Glass Co., Ltd.. Invention is credited to Hananaka, Kenjiro.
Application Number | 20020186922 10/165512 |
Document ID | / |
Family ID | 19014997 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020186922 |
Kind Code |
A1 |
Hananaka, Kenjiro |
December 12, 2002 |
Optical module, alignment method of optical module, and alignment
device of optical module
Abstract
A light coupling means 4 is provided with a collimator lens 41
and a half mirror 42. After reference light is changed to parallel
light by the collimator lens 41, the parallel light is folded back
by the half mirror 42 in the same direction as object light emitted
from a microlens array 32 to overlap the object light, thereby
generating interference patterns.
Inventors: |
Hananaka, Kenjiro;
(Osaka-shi, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Nippon Sheet Glass Co.,
Ltd.
Osaka-shi
JP
|
Family ID: |
19014997 |
Appl. No.: |
10/165512 |
Filed: |
June 7, 2002 |
Current U.S.
Class: |
385/33 ;
385/31 |
Current CPC
Class: |
G02B 6/32 20130101; G02B
6/4225 20130101; G02B 6/4227 20130101; G02B 6/3672 20130101 |
Class at
Publication: |
385/33 ;
385/31 |
International
Class: |
G02B 006/32; G02B
006/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2001 |
JP |
2001-173556 |
Claims
What is claimed is:
1. An alignment method of an optical module comprising an optical
fiber array in which a plurality of optical fibers are disposed in
one or two-dimensional manner and a microlens array in which a
plurality of microlens are disposed in one or two-dimensional
manner for aligning optical axes of the optical fibers and the
microlens corresponding the optical fibers, the alignment method
further comprising the steps of: splitting a laser beam emitted
from a laser beam source into object light and reference light;
causing the object light to enter at least one of the plurality of
optical fibers and to emit from the microlens array; overlapping
the emitted object light and the reference light to generate
interference patterns, and making fine adjustments to a relative
position of the optical fiber array and the microlens array based
on the interference patterns.
2. The alignment method of an optical module according to claim 1,
wherein the object light is caused to enter two optical fibers and
to overlap the reference light so as to generate two interference
patterns, wherein fine adjustments are made to a relative position
of the optical fiber array and the microlens array to allow these
two interference patterns to approximate.
3. The alignment method of an optical module according to claim 2,
wherein a wave front phase analyzed from interference fringes of
the two interference patterns are caused to approximate.
4. The alignment method of an optical module according to claim 1,
wherein a phase of the object light or the reference light is
shifted to change the interference patterns.
5. The alignment method of an optical module according to claim 1,
wherein the interference patterns are observed at a position spaced
apart a predetermined distance from the microlens array.
6. The alignment method of an optical module according to claim 5,
wherein the position for observing the interference patterns is the
position where the wave front phase is approximate to a plane
wave.
7. The alignment method according to claims 1 through 6, wherein
the optical module is provided by aligning the optical fiber array
and the microlens array, and the optical fiber array and the
microlens array are bonded together in such a condition.
8. An alignment device of an optical module comprising an optical
fiber array in which a plurality of optical fibers are disposed in
one or two-dimensional manner and a microlens array in which a
plurality of microlens are disposed in one or two-dimensional
manner for aligning optical axes of the optical fibers and the
microlens corresponding to the optical fibers, the alignment device
further comprising: splitting means for splitting a laser beam
emitted from a laser beam source into object light and reference
light; means for guiding the object light to the optical fibers;
light coupling means for overlapping the object light emitted from
the microlens array and the reference light to generate
interference patterns; light observation means for observing the
interference patterns; and means for making fine adjustments to a
relative position of the optical fiber array and the microlens
array based on the interference patterns.
9. The alignment device of an optical module according to claim 8,
wherein another light coupling means for allowing the object light
to enter the two optical fibers forming the optical fiber array is
provided in an optical path of the object light.
10. The alignment device of an optical module according to claim 8,
wherein a phase shifting means is provided in an optical path of
the reference light or in an optical path of the object light
emitted from the microlens array.
11. The alignment device of an optical module according to claim 8,
wherein the light observation means is provided with an image input
element such as a CCD camera or a camera tube, and an optical
system for forming an image in a position spaced apart a
predetermined distance from the microlens on the image input
element.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an alignment method for
aligning optical axes of an optical fiber array and a microlens
array which form an optical module, the optical module aligned by
the alignment method, and a device for performing the alignment
method.
[0003] 2. Description of the Prior Art
[0004] An optical module for optical communication which coupled an
optical fiber array to a microlens array is known. This module is
provided to cause light from a light emitting diode to enter the
microlens through an optical fiber and to take it out as collimated
light or to cause the collimated light to enter the optical fiber
through the microlens.
[0005] In such an optical module, it is essential for the optical
axes of the optical fiber and the microlens to agree with each
other for improvement of communication accuracy. An optical axis
adjustment method for this optical module is disclosed in Japanese
Unexamined Patent Publication No. Hei 9-061666.
[0006] In this prior art, a mask having a mesh-shaped pattern of
the same array pitch as that of an optical fiber array and a
collimation lens array (i.e., microlens array) is provided in front
of a detector which detects light beam shape. Light is caused to
enter the collimation lens array through the optical fiber array,
and the light emitted from the collimation lens array and passed
without being blocked off by the mask is sensed by the detector. A
relative position of the optical fiber array and the collimation
lens array is adjusted so that the light beam shape corresponding
to each optical fiber can be uniform.
[0007] However, even though the optical axis adjustment is made
according to the conventional method stated above, it is only
possible to make extremely rough adjustment. Further, even when the
relative position of the optical fiber array and the collimation
lens array is adjusted, it is still not clear in which direction
and to which extent the adjustment should be made.
SUMMARY OF THE INVENTION
[0008] To solve the problems stated above, an alignment method of
an optical module according to the present invention is provided,
in which alignment of the optical module comprising an optical
fiber array in which a plurality of optical fibers are disposed in
one or two-dimensional manner and a microlens array in which a
plurality of microlenses are disposed in one or two-dimensional
manner is made, characterized in that a laser beam emitted from a
laser beam source is split into object light and reference light
and the object light is caused to enter at least one of the
plurality of optical fibers and to emit from the microlens array,
wherein the reference light is provided to overlap the emitted
object light so as to generate interference patterns, thereby
making fine adjustments to relative position of the optical fiber
array and the microlens array based on the interference
patterns.
[0009] An alignment device of the optical module according to the
present invention comprises a means for splitting a laser beam from
a laser beam source into object light and reference light, a means
for guiding the object light to an optical fiber, a light coupling
means for overlapping the object light emitted from a microlens
array and the reference light each other to generate interference
patterns, light observation means for observing the interference
patterns, and a means for make fine adjustment to relative position
of an optical fiber array and the microlens array based on the
interference patterns.
[0010] In this manner, the interference patterns of the object
light and the reference light greatly change even by slight shift
or deviation of the optical axis. Accordingly, it is possible to
precisely make fine adjustments to the optical axis using these
interference patterns.
[0011] An efficient alignment method is provided in which the
object light is caused to enter two optical fibers and to overlap
reference light so as to generate two interference patterns,
wherein fine adjustments are made to relative position of the
optical fiber array and microlens array to allow the two
interference patterns to approximate. In this case, it is desirable
that the two interference patterns be the same with each other, but
they don't have to be completely the same.
[0012] To allow the object light to enter the two optical fibers,
the object light split by a light splitter is caused to enter the
two optical fibers forming the optical fiber array through a
coupling member.
[0013] For comparison of the two interference patterns, wave front
phase analysis software is installed within a control device such
as a personal computer, wherein the wave front phase is analyzed
from the interference fringes of the two interference patterns to
allow these wave front phases to approximate.
[0014] It is possible to know the direction and tendency of the
optical axis shift or deviation by changing the interference
patterns. To change the interference patterns, for example, a phase
of the object light or reference light can be shifted. To shift the
phase, a phase shifting means is provided in the optical path of
the reference light or the optical path of the object light emitted
from the microlens array.
[0015] For observational interference patterns, the interference
patterns on the position spaced away predetermined distance from
the microlens array are used. Specifically, the laser beam is a
Gausian beam provided with a beam waist. When the beam waist
position is set to be an observation position, the wave front phase
becomes a plane wave.
[0016] The light observation means shall be provided with an image
input element such as a CCD camera or a camera tube, and an optical
system for forming an image in a position spaced apart a
predetermined distance from the microlens on the image input
element.
[0017] If the alignment is made using the above method and device,
the target optical module can be obtained by bonding the optical
fiber array and the microlens array together in such a
condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings.
[0019] FIG. 1 is a schematic diagram showing a device for use in an
alignment method of the present invention;
[0020] FIG. 2 (a) is a side view showing one example of an optical
module and FIG. 2 (b) is a view taken in the direction of the arrow
A of FIG. 2 (a) showing an optical fiber array;
[0021] FIG. 3 (a) is a view explaining the wave front of object
light in the case where an optical axis of an optical fiber agrees
with that of a microlens and FIG. 3 (b) is a view explaining the
wave front of object light in the case where the optical axis of
the optical fiber does not agree with that of the microlens;
[0022] FIGS. 4 (a) to (c) are views showing the conditions in which
object light and reference light overlap each other and
interference patterns caused by the overlapping conditions;
[0023] FIGS. 5 (a) and (b) are views showing the conditions in
which two interference patterns are displayed on a monitor;
[0024] FIG. 6 is a view similar to FIG. 1 showing another
embodiment;
[0025] FIG. 7 (a) is a view schematically explaining the maximum
shift of a wave front phase;
[0026] FIG. 8 is a view showing interference patterns, a phase
shift of a wave front, and a shift amount of an optical axis;
and
[0027] FIG. 9 is a view showing another embodiment of an optical
module.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Preferred embodiments of the present invention will now be
described with reference to the accompanying drawings. FIG. 1 is a
schematic diagram of a device for use in an alignment method of the
present invention. Reference numeral 1 is a semiconductor laser
serving as a light-emitting source, 2 is a light-splitting means
for splitting a laser beam from the semiconductor laser into object
light and reference light, and 3 is an optical module. 4 is a light
coupling means for overlapping the object light transmitted through
the optical module and the reference light each other, and 5 is a
light observation means for observing an interfering pattern caused
by overlapping the object light and the reference light each
other.
[0029] The light-splitting means 2 is provided with a coupling lens
21 and a beam splitter 22. A laser beam is split into object light
and reference light by the beam splitter 22. The object light is
connected to two optical fibers of an optical fiber array 31
forming the optical module 3 through a single mode optical fiber
23, a light-branching section 24, and a coupling 25. The reference
light is fed to the light coupling means 4 through a single mode
optical fiber 26.
[0030] FIG. 2 (a) is a side view showing one example of an optic
module and FIG. 2 (b) is a view taken in the direction of the arrow
A of FIG. 1 (a) showing an optical fiber. The optical module 3 is
composed of the optical fiber array 31 and a microlens array 32.
The optical fiber array 31 and the microlens array 32 are firmly
secured to the optical module 3 after completed as a finished
product. However, one of them (i.e. the optical fiber array 31) is
slightly movable in the direction of X, Y, and Z axes and rotatable
around each axis by a known means because adjustment of the optical
axis is conducted in the present invention.
[0031] The optical fiber array 31 has a silicon substrate 33
provided with V-grooves at regular intervals in one or
two-dimensional shape, and single mode optical fibers 34 are
secured in the grooves. The optical fiber array 31 is not
necessarily limited this construction, but it may be formed in such
a manner that a stainless steel substrate or glass substrate is
formed with openings in advance into which the optical fibers are
inserted and secured.
[0032] The microlens array 32 has a glass substrate 35 provided
with a plurality of microlenses 36 corresponding to the optical
fibers 34. The microlens 36 can be formed by 2P (photopolymer)
molding method using ultraviolet ray-setting resin, a method
whereby an etching is effected on a glass substrate surface through
a mask to form many recessions into which resin of high refractive
index is filled, a method whereby ions are diffused on a glass
substrate surface through a mask to change a refractive index,
etc.
[0033] The light coupling means 4 is provided with a collimator
lens 41 and a half lens 42. After reference light is changed to
parallel light by the collimator lens 41, the parallel light is
folded back by the half mirror 42 in the same direction as object
light emitted from the microlens array 32 to overlap the object
light, thereby generating an interference pattern.
[0034] The light observation means 5 is composed of a CCD camera or
a camera tube provided with an image formation lens 51 and a light
receiving element 52. The interference pattern on an observation
surface on the downstream side of the light coupling means 4 is
formed on the light receiving element 52 and displayed on a monitor
53.
[0035] The interference pattern will now be described. FIGS. 3 (a)
and (b) are views showing wave fronts of the object light. FIG. 3
(a) show the case where an optical axis of the optical fiber 34
agrees with that of the microlens 36 while FIG. 3 (b) shows the
case where the optical axis of the optical fiber 34 does not agree
with that of the microlens 36. FIGS. 4 (a) through (c) are views
showing the overlapping conditions of the object light and the
reference light, and the interference patterns caused by such
conditions.
[0036] As shown in FIG. 3 (a), when the optical axis of the optical
fiber 34 agrees with that of the microlens 36 and the observation
surface is situated on the beam waist of the object light, the wave
front of the object light becomes parallel to that of the reference
light as shown in FIG. 4 (a). In this case, the interference fringe
(i.e., interference pattern) is not visible.
[0037] As shown in FIG. 3 (b), when the optical axis of the optical
fiber does not agree with that of the microlens, but the
observation surface is situated on the beam waist of the object
light, the object light is a plane wave, but not parallel to the
wave front of the reference light as shown in FIG. 4 (b). In this
case, linear interference fringes are generated.
[0038] As shown in FIG. 3 (c), when the optical axis of the optical
fiber agrees with that of the microlens, but the observation
surface is situated off the beam waist of the object light, the
wave front of the object light becomes a spherical wave. In this
case, concentric interference fringes are generated as shown in
FIG. 4 (c).
[0039] The interference fringes show equiphase line (i.e., contour
line) of the wave front of the object light generated by causing
the object light to interfere with the reference light. The
narrower the interval between the equiphase lines at the
interference fringes of the plane wave, the greater the deviation
or shift in the direction perpendicular to the optical axis.
[0040] The spherical wave is generated because the observation
surface is situated off the beam waist. Accordingly, as shown by
the arrow in FIG. 3 (c), the interference fringes can be removed by
relatively moving the optical fiber array in the direction of the
optical axis.
[0041] Meanwhile, in the embodiment, since the object light is
caused to enter two optical fibers, as shown in FIG. 5 (a) or (b),
two interference patters P1 and P2 are displayed on a monitor.
According to the example shown in FIG. 5 (a), the optical axes of
the optical fiber and microlens corresponding to the interference
pattern P1 shift in the direction of X-X while no shift is produced
between the optical axes of the optical fiber and microlens. On the
other hand, according to the example shown in FIG. 5 (b), the
optical axes of the optical fiber and microlens corresponding to
the interference pattern P1 shift in the direction of U-U while the
optical axes of the optical fiber and microlens corresponding to
the interference pattern P2 shift in the direction of V-V.
[0042] In this manner, when the interference patters more than two
(of course, the interference patterns can be formed using all the
optical fibers and microlenses) are generated, adjustment may be
made to make the least square error of all the shift or deviation
minimal or to make the worst shift or deviation minimal.
[0043] FIG. 6 is a view similar to FIG. 1 showing another
embodiment. In this embodiment, a phase-shifting means 6 is
provided in an optical path of the reference light. This
phase-shifting means 6 is caused to move a mirror 61 which reflects
the parallel light from the collimator lens 41 toward the half
mirror 42 by .lambda./4, .lambda./2 or 3 .lambda./4 by a
piezoelectric element 62 such as PZT so that a plurality of
interference patterns can be image-input into the light observation
means 5 for analysis. In this manner, it is possible to precisely
quantify the phase shift of the wave front including a sign of plus
and minus of the phase shift (the so-called "Fringe Scanning
Method" or "Phase-shifting Method").
[0044] Next, quantification of the shifting dimensions and
direction of the optical axis will be described. In FIG. 7, if the
shift amount of the optical axis between the optical fiber and the
lens is .DELTA.y, the distance between the optical fiber and the
lens is d0, the beam diameter of the observation surface is e, and
the wavelength is .lambda. and provided that no shift is produced
in the direction of the optical axis for the sake of convenience,
the maximum shift or deviation W of the wave front phase (unit:
wavelength .lambda.) is expressed in he following formula (1):
W=(e.multidot..DELTA.y)/(d0.multidot..lambda.) (1)
[0045] When the phase shift observed from the formula (1) is W, the
shift amount .DELTA. y of the optical axis is expressed in the
following formula (2):
.DELTA.y=W.multidot.d0.multidot..lambda./e (2)
[0046] For example, assuming that the interference fringes shown in
FIG. 8 (a) are obtained by making observation at both ends of the
array, the wave front phase shown in FIG. 8 (b) is obtained from
this interference fringes. As shown in FIG. 8 (c), each optical
axis shift amount .DELTA.y1, .DELTA.y2 at both ends of the array
including the direction can be found.
[0047] Specifically, if d0=1 mm, .lambda.=1.55 .mu.m, and e=200
.mu.m, .DELTA.y1=38.75 .mu.m and .DELTA.y2=15.5 .mu.m.
[0048] In the present embodiment, the optical module whereby the
light emitted from the microlens array becomes the parallel light
is shown, but as shown in FIG. 9, light may be caused to enter the
optical module in which object light has a focal point at a
predetermined position.
[0049] Further, the optical path for providing the phase shifting
means 6 can be that for object light.
[0050] As described above, according to the present invention, it
is possible to precisely adjust the shift or deviation of the
optical axes of the optical fiber and the microlens corresponding
thereto. It is also possible to make an alignment operation easier
because adjustment is made by making use of the interference
fringes.
* * * * *